The present invention relates to an image scanner which includes a charge coupled device (CCD) of a low pixel density, and particularly to an image scanner using the low-pixel-density CCD to achieve a better scanning quality than it could. The better scanning quality can be obtained by performing a small-amount shift of the CCD.
Due to the improvement on manufacturing techniques and the reduction of cost, an image scanner becomes a popular peripheral equipment for a personal computer. Meanwhile, owing to the enhancement of the processing speed of the computer itself and the increasing requirement of users on the scanning quality, the resolution of an image scanner is getting higher and higher. Therefore, it is a trend for the manufacturers of image scanners to improve the resolution as possible as they can.
The resolution of an image scanner is generally expressed by X DPIxc3x97Y DPI wherein DPI means Dot Per Inch. the number Y indicates the count of scanning lines per inch, which is determined by the moving speed of a carriage driven by a stepping motor along the Y-axis. The number X represents the optical resolution which is determined by the amplifying rate of the lens device and the pixel number of the photoelectric converting device such as a charge coupled device (CCD). For X=600 as an example, it means that each inch of the scanned image in the X-direction, through the focusing and contraction of the lens device, is exposed by 600 pixels of the CCD.
In order to enhance the optical resolution of the image scanner, a software interpolation method or a CCD of a high pixel number can be optionally used. If a software interpolation method is used to simulate a high-level state, no additional cost for hardware equipment is needed but there is more or less distortion for the obtained image. If a CCD of a high pixel number is used, the cost of the resulting image scanner will multiply increase. Therefore, various researches are performed in order to develop an image scanner of higher resolution, better scanning quality, and lower cost.
The Taiwanese Patent Publication No. 313286 filed Jul. 29, 1996, and incorporated herein for reference, discloses a twice-scanning process by using a low-pixel-number CCD to scan a half of a document, and then moved along the X-direction to scan the other half of the document so as to double the resolution compared to the only once scanning operation by a CCD of the same pixel number. This process, however, still has disadvantages. First of all, the long distance movement of the light-program device including the CCD and the lens device across a half of the document along the X-direction has adversely effect on positioning precision. In addition, the switching device for driving the light-program device to move that long requires a complicated and bulky structure, and thus consumes a lot of power. Further, it takes time to move such a long distance.
Therefore, an object of the present invention is to provide an image scanner using a low-pixel-density CCD, which is moved in a pixel level, to achieve a high-pixel-density scanning quality in an efficient way.
A first aspect of the present invention relates to an image scanner for reading and converting an image of an object into digital image data. The image scanner includes a photoelectric sensing device including a plurality of sensing pixels arranged at equal spaces for converting an optical signal from the object into an electric signal, and a shifting device connected to the photoelectric sensing device for driving the photoelectric sensing device from a first position to a second position along an X-direction to obtain a first electric signal and a second electric signal, respectively, wherein a distance between the first and the second positions is less than a distance between two adjacent sensing pixels, and the first and the second electric signals are alternately arranged and converted to form the digital image data.
In an embodiment, the photoelectric sensing device includes a lens device for focusing and contracting the optical signal, a linear charge coupled device consisting of the plurality of sensing pixels which senses the focused and contracted optical signal to generate the electric signal, and a holder for mounting thereon the lens device and the linear charge coupled device. The holder is driven by the shifting device to allow the lens device and the linear charge coupled device to be moved together from the first position to the second position.
Generally, the image scanner further includes a mirror set arranged upstream of the lens device for transmitting the optical signal from the object to the lens device, and a carriage housing mounted therein the mirror set, the photoelectric sensing device and the shifting device, and moved along a Y-direction to scan the object.
In an embodiment, the shifting device includes a guiding track secured on the carriage housing for guiding the holder along the X-direction, a first magnetic element secured on the holder, and a second magnetic element secured on the carriage housing and cooperating with the first magnetic element to generate a magnetic force. The magnetic force includes alternate attracting and repelling forces between the first and the second magnetic elements so as to reciprocate the holder between the first and the second positions along the guiding track.
Preferably, the shifting device further includes two stoppers located by two opposite sides of the holder in order to further assure that the holder reciprocates between the first and the second positions.
Preferably, the first magnetic element is a first permanent magnet, and the second magnetic element includes an electric motor and a second permanent magnet. The second permanent magnet is coupled to and driven by the electric motor to rotate relative to the first permanent magnet to switch the magnetic force between the attracting and repelling forces so as to reciprocate the holder.
Preferably, the distance between the first and the second positions is equal to a half of the distance between two adjacent sensing pixels.
A second aspect of the present invention relates to an image scanner which includes a photoelectric sensing device including a plurality of sensing pixels arranged at equal spaces for converting an optical signal from the object into an electric signal, a carriage housing for mounting therein the photoelectric sensing device, and a shifting device connected to the carriage housing for driving the carriage housing to move the photoelectric sensing device from a first position to a second position along an X-direction. The photoelectric sensing device is actuated at the first and the second positions to obtain a first electric signal and a second electric signal, respectively. A distance between the first and the second positions is less than a distance between two adjacent sensing pixels. The first and the second electric signals are alternately arranged and converted to form the digital image data.
In an embodiment, the photoelectric sensing device includes a lens device for focusing and contracting the optical signal, a mirror set arranged upstream of the lens device for transmitting the optical signal from the object to the lens device, and a linear charge coupled device consisting of the plurality of sensing pixels which senses the focused and contracted optical signal to generate the electric signal.
Broadly, the term xe2x80x9cimage scannerxe2x80x9d used herein includes any suitable digital image pickup device which scanning an object and converting the image of the object into digital image data. Further, the image scanner can be a reflective or a transmissive or a dual-mode image scanner.